1. Field of the Invention
This invention relates to a data processing device and, more particularly, to a data processing device of the kind handling a sequence of data obtained by sampling an analog information signal to process each of the data included in the data sequence.
2. Description of the Prior Art
Generally, data obtained by sampling an analog signal include some incorrect data resulting from errors and drop-outs which arise, for example, during transmission for recording or reproduction. If incorrect rate data singly arises, the general practice is to have the waveform of the original analog signal proximately reproduced by replacing the incorrect data with an interpolation data which is obtained from correct data located before and/or after the incorrect data. For example, an incorrect data arising among data obtained by sampling an audio signal is replaced with an interpolation data which is obtained by utilizing data located before and/or after the data in question. The known methods for this purpose include: A pre-hold method in which a data located immediately before an incorrect data is used as an interpolation data; an average value interpolation method in which an average value obtained from data located immediately before and after an incorrect data, is used as an interpolation data; and a tertiary interpolation method in which interpolation data is obtained from at least four data located in the neighborhood of an incorrect data.
As to the degree of proximity of the interpolation data to the original data, the pre-hold method is the poorest; the average value interpolation method is better and the tertiary interpolation method is the best of the three methods. However, the scale of the hardware arrangement required by these methods increases as the proximity increases. Particularly, in the case of the tertiary interpolation method, there must be at least two correct data before an incorrect data and two correct data after the correct data. Then, the four data, which thus span a long time period, must be computed by a large-scaled computing circuit in obtaining the interpolation data. This interpolation method thus requires complex hardware arrangement. It is, therefore, not generally employed except where an especially highly accurate interpolation is required and thus is not used for household appliances.
Whereas, the pre-hold method is advantageously characterized by the extremely simple arrangement required thereby. However, as shown in FIG. 1 of the accompanying drawings, the interpolation data obtainable by this method is not close to the original analog signal. In FIG. 1, the original analog signal is depicted with a broken line, correct data with a mark "o", an ideal interpolation data with a mark "x" and the interpolation data obtainable by the pre-hold method with a mark ".DELTA.".
The average value interpolation method can be carried out with a simple circuit arrangement, as will be described later. However, the proximity of the interpolation data of that method to the original analog signal is insufficient as shown in FIG. 2. In FIG. 2, the broken line, the marks "o", "x" and ".DELTA." are used in the same manner as in FIG. 1.
Meanwhile, in the event of a plurality of consecutive incorrect data, the insufficient proximity of the interpolation data becomes poorer than in the case of a single occurrence of an incorrect data. In view of this, efforts have been exerted to avoid a consecutive occurrence of a plurality of incorrect data in recording, reproduction and communication by contriving a special arrangement of data and by including some error correction data, such as parity words or the like, in the data arrangement. Despite the above-stated efforts, however, a consecutive occurrence of a plurality of incorrect data is not actually sufficiently eliminatable. With the above-stated specially contrived data arrangement employed, two or three incorrect data tend to consecutively occur.
FIGS. 3 and 4 show the interpolation data obtained by the prior art methods in cases where two incorrect data consecutively occur. In the case of FIG. 3, interpolation data are produced by a device which obtains an interpolation data by the pre-hold method when a single incorrect data occurs. In FIG. 4, interpolation data are produced by a device which obtains interpolation data by the average value interpolation method in the event of a single occurrence of an incorrect data.
Referring to FIG. 3, in a device using the pre-hold method, all incorrect data are replaced with interpolation data of the same value as a data obtained at a point of time t2, which immediately precedes these consecutive incorrect data. Referring to FIG. 4, the device using the average value interpolation method replaces the last of the consecutive incorrect data with an interpolation data having an average value of correct data immediately before and after the consecutive occurrence of the incorrect data and the other of the consecutive incorrect data with an interpolation data of a value which is the same as that of the correct data obtained immediately before them. As shown in FIGS. 3 and 4, the interpolation data obtainable by these prior art methods clearly impair the waveform of the original analog signal. If three or more consecutive incorrect data occur, this undesirable tendency becomes more salient.
It is, of course, possible to obtain, even in the event of such a consecutive occurrence of low reliability or incorrect data, interpolation data for them in closer proximity to the original signal by using and computing several correct data located before and after these consecutive low reliability data. However, as mentioned in the foregoing, that method necessitates use of a more complex hardware arrangement and thus is not practical.